Movements which can be easily performed by an able-bodied person are often extremely difficult to perform for a physically disabled person having lost his/her muscular strength or an elderly person having deteriorated muscular strength. Therefore, development of various power assisting apparatuses are being promoted these days for assisting or substituting for movement of such people.
One of such power assisting apparatuses is, for example, a wearable type movement assisting apparatus (hereinafter simply referred to as “movement assisting apparatus”) that is worn by the user (hereinafter referred to as “wearer”).
Such types of movement assisting apparatuses include one that is developed with a configuration including a myoelectric potential sensor (detecting part) for detecting a myoelectric potential signal (biosignal) associated with muscular activity of the wearer and an actuator for applying assisting power to the wearer (for example, non-patent document 1).
This movement assisting apparatus has a characteristic of driving the actuator (e.g. motor) based on detection results from the detecting part and controlling the actuator by a computer for applying assisting force (assisting power) according to the will of the wearer. Accordingly, the movement assisting apparatus can apply assisting force to the wearer based on the will of the wearer and provide an assisting force required for the movement of the wearer in cooperation with the movement of the wearer.
Meanwhile, the above-described movement assisting apparatus generates an assisting force for satisfying a necessary correlation with respect to myoelectric potential signals emitted from the wearer, for example, by supplying control signals having a predetermined correlation with respect to amplified detection signals of a myoelectric potential sensor to a driver circuit that controls the actuator.
That is, since myoelectric signals and movement corresponding to muscular activity of the wearer have a positive correlation and their proportion becomes a certain value, it is necessary to apply an assisting force corresponding to myoelectric signals so as to satisfy such relationships. In other words, unless the assisting force of the movement assisting apparatus satisfies a certain relationship with respect to myoelectric potential signals, the assisting power applied to the wearer may become too much or too little, and may adversely affect the user.
The myoelectric potential signals emitted by the wearer are weak electric signals. Furthermore, the proportional relationship between myoelectric potential signals and muscular strength corresponding to the myoelectric potential signals differs depending on each individual. Moreover, the electric resistance value of skin is not constant even for the same person depending on his/her daily condition. Accordingly, there are many cases where the myoelectric potential signals and the muscular strength generated according to the myoelectric potential signals are not constant. Therefore, the movement assisting apparatus is installed with a so-called calibration apparatus for correcting a controlled variable with respect to an actuator by multiplying the variable by a predetermined coefficient (parameter) to obtain a control signal. More specifically, a calibration apparatus is provided for associating myoelectric potential signals and assisting force with a certain relationship and performing correction by using a coefficient (parameter) in a case where the movement assisting apparatus is worn by the wearer. This calibration apparatus is configured to correct a controlled variable by obtaining myoelectric potential signals generated when a certain amount of load is applied to the wearer and deriving and changing the above-described coefficient (parameter) in accordance with the corresponding relationship between the load and the myoelectric potential signals.
In a case where the calibration apparatus changes the load applied to the wearer step by step and provides muscular strength to the wearer for counterbalancing the load in each step, the calibration apparatus can associate myoelectric signals and assisting power to establish a certain relationship based on the corresponding relationships between the load and the myoelectric potential signals of each step.
As a method of changing the load applied to the wearer step by step, there is a method of preparing poises of various weights and exchanging the poises whenever a surface myoelectric signal is detected, or a method of connecting a coil spring to the leg of the wearer and changing the amount of expansion of the coil spring step by step.
With the movement assisting apparatus including a calibration apparatus using these methods, myoelectric potential signals and assisting power can be reliably associated by a certain relationship according to necessity. Accordingly, the assisting force applied to the wearer can be prevented from becoming too much or too little.    Non-Patent Document 1: Takao Nakai, Suwoong Lee, Hiroaki Kawamoto and Yoshiyuki Sankai, “Development of Power Assistive Leg for Walking Aid using EMG and Linux,” Second Asian Symposium on Industrial Automation and Robotics, BITECH, Bangkok, Thailand, May 17-18, 2001